<template>
    <ul class="list">
        <li class="item" v-for="item of letters" :key="item" @click="handleLetterClick" @touchstart="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd" :ref="item">{{item}}</li>
    </ul>
</template>

<script>
    export default {
        name: "CityAlphbet",
        props: {
            cities: Object
        },
        data() {
            return {
                touchStatus: false,
                startY: 0,
                timer: null
            }
        },
        updated() {
            this.startY = this.$refs['A'][0].offsetTop
        },
        computed: {
            letters() {
                const letters = []
                for (let i in this.cities) {
                    letters.push(i)
                }
                return letters
            }
        },
        methods: {
            handleLetterClick(e) {
                this.$emit('change', e.target.innerText)
            },
            handleTouchStart() {
                this.touchStatus = true
            },
            handleTouchMove(e) {
                if (this.touchStatus) {
                    if (this.timer) {
                        clearTimeout(this.timer)
                    }
                    this.timer = setTimeout(() => {
                        const touchY = e.touches[0].clientY - 79
                        const index = Math.floor((touchY - this.startY) / 20)
                        if (index >= 0 && index < this.letters.length) {
                            this.$emit('change', this.letters[index])
                        }
                    }, 16)
                }
            },
            handleTouchEnd() {
                this.touchStatus = false
            }
        }
    };
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl';
.list
    position absolute
    top 1.58rem
    right 0
    bottom 0
    width .4rem
    display flex 
    flex-direction column
    justify-content center
    .item
        text-align center
        line-height .4rem
        color $bgColor

</style>

